(a) Field of the Invention
The present invention relates to a thin film transistor array panel and its manufacturing method.
(b) Description of the Related Art
Flat panel displays, such as liquid crystal displays (LCDs) and organic light emitting diode (OLED) displays, include several pairs of field generating electrodes and electro-optical active layers interposed between the field generating electrodes. The LCD includes a liquid crystal layer as an electro-optical active layer, and the OLED includes an organic emission layer as the electro-optical active layer.
One electrode of a pair of field generating electrodes, i.e., a pixel electrode, is commonly connected to a switching element for transmitting electrical signals to the pixel electrode, and the electro-optical active layer converts the electrical signals to optical signals to display an image.
A thin film transistor (TFT) having three terminals is used for the switching element in the flat panel display, and a plurality of signal lines such as gate lines and data lines are also provided on the flat panel display. The gate lines transmit signals for controlling the TFTs and the data lines transmit signals that are applied to the pixel electrodes.
The lengths of the gate and data lines increase with the LCD size. As the line lengths increase, resistance on the lines increase and cause a signal delay or a voltage drop. Wiring made of a material having low resistivity, such as aluminum or copper, is desired to overcome these problems caused by increased resistance on the lines.
However, aluminum lines have their disadvantages. When a signal line made of aluminum directly contacts a semiconductor layer of a thin film transistor, aluminum atoms diffuse into the semiconductor layer and lower the performance of the thin film transistor. Also, a signal line made of aluminum has a poor contact property with other materials such as indium-tin-oxide (ITO), and thus a pixel electrode of ITO in direct contact with the aluminum signal line may receive imperfect signals from the aluminum signal line.